The invention relates to a method of building a composite using reinforcement cords and composites made using such method.
It is a continuing goal in the tire industry to reduce the cost of manufacturing tires without sacrificing tire properties. One way in which cost can be reduced is by reducing the handling cost involved in material preparation when strength and durability characteristics are not sacrificed, or when the material is used in a tire component where strength and durability properties need not be significant.
In the prior art, tire reinforcement cords are twisted; first the yarn (ply) used to make the cord, and then the cord itself, to increase the durability and fatigue resistance of the cord. The ply twisting and the cord twisting are both time and energy consuming operations, and handling costs are reduced by eliminating or reducing one or both of these expensive steps.
For several years, Goodyear has reduced the expense of reinforcement cords for certain tires by reducing the yarn twist while maintaining the conventional cord twist. For example, when a Z ply twist of 197 tpm (turns per meter) (5 tpi (turns per inch)) is used, an S cord twist of 334 to 472 tpm (8.5 to 12 tpi) is used. In theory, it is believed that yarn twists of 118 to 472 tpm (3 to 12 tpi) can be used as long as the twist multiplier (TM) is 10 or less and the yarn twist is maintained less than the cord twist. It has been found, however, that treated fabric and reinforced rubber composites made with such cords are difficult to process since the residual torque, caused by the unbalanced twist in the cords, causes the treated fabric, and sometimes the fabric reinforced composite, to roll up at the edges, and the cost savings obtained by the reduced twist in the ply (yarn) is partly or totally lost due to the increased handling cost of the fabric and the composite.
In certain tires, specifications call for reinforced components having cords with an S twist to alternate with cords having a Z twist in the reinforced structure. In the conception of the invention, the inventors have theorized that if reinforcement cords with a reduced yarn twist are alternated S and Z in a fabric, the torques applied to the treated fabric and a resulting fabric reinforced composite by the S and Z cords would neutralize each other and eliminate the handling problems, thereby reducing the cost of tires specifying S and Z reinforcement.
A method of making an elastomeric composite containing reinforcement cords comprises the steps of, (a) applying a twist to a first yarn of 118 to 315 tpm (3 to 8 tpi) in the S or Z direction, (b) gathering a plurality of the first yarns into a first cord and applying an S twist to the cord of 157 to 551 tpm (4 to 14 tpi) wherein the cord twist is greater than the yarn twist, (c) gathering a plurality of the first yarns into a second cord and applying a Z twist to the cord of 157 to 551 tpm (4 to 14 tpi) where the cord twist is greater than the yarn twist, (d) calendering the first and second cords into an elastomer wherein nxc3x97 TM of S cords substantially equals nxc3x97 TM of Z cords, wherein n is the number of cords and TM is the twist multiplier of the cords as defined by
TM=((tpmxc3x970.0254)xc3x97(dTex/1.111))/73
where dTex represents the linear density of the bulk greige yarn, and tpm is the twist of the cord in turns per meter. It is preferred that in the making of the fabric used to make a reinforced rubber composite, no more than 5 S cords or 5 Z cords are adjacent to each other.
The method may further comprise the steps of, (a) applying an S twist to the yarn, and (b) applying a Z twist to the cord, or (a) applying a Z twist to the yarn, and (b) applying an S twist to the cord.
In alternative embodiments, the method may comprise the steps of (a) applying an S twist to the yarn, and (b) applying an S twist to the cord or (a) applying a Z twist to the yarn, and (b) applying a Z twist to the cord.
The method may also comprise specific cord twist and specific cord constructions. For example, fabrics and reinforced rubber composites have been made by (a) applying a yarn twist of 197 tpm (5 tpi), and (b) applying a cord twist of 394 tpm (10 tpi). Also, cord constructions have been made by gathering 3 yarns into each of the variously twisted cords.
Also provided is an elastomeric composite ply comprising an elastomer matrix and substantially parallel reinforcing cords wherein said reinforcing cords comprise a plurality of yarns having an S or Z twist of 118 to 315 tpm (3 to 8 tpi), wherein some of the cords have a Z twist of 157 to 551 tpm (4 to 14 tpi) wherein the cord twist is greater than the yarn twist, and some of the cords have an S twist of 157 to 551 tpm (4 to 14 tpi) wherein the cord twist is greater than the yarn twist, made by the method of the invention.
Also provided is a pneumatic tire made using a reinforcing ply of the invention.